Apparatus and methods for removing and installing a selected nozzle segment of a gas turbine in an axial direction

ABSTRACT

Nozzle segments are secured to a retention ring against circumferential rotation by anti-rotation pins extending generally axially between the outer bands of the nozzle segments and the retention ring. Retention plate segments overlie the ends of the pins, preventing axial removal thereof. To remove a selected nozzle segment, inner diameter retention plate segments and selected retention plate segments are removed, the latter exposing the ends of the pins for axial withdrawal. Upon removal of a predetermined number of pins, the nozzle segments adjacent the selected segment are displaced away from the latter segment to open a gap between the selected segment and adjacent segments whereby the selected segment can be removed in an axial direction.

BACKGROUND OF THE INVENTION

The present invention relates to apparatus and methods for removing andinstalling a selected nozzle segment relative to a nozzle retention ringof a gas turbine and particularly relates to axially orientedanti-rotation pins for preventing circumferential movement of the nozzlesegments and enabling removal and insertion of the anti-rotation pins inan axial direction to facilitate removal and installation of a selectednozzle segment without removal of the casing.

In gas turbines, the nozzle stages are typically formed by an annulararray of nozzle segments spaced circumferentially one from the otherabout the axis of the turbine. For example, in the first stage of theturbine, the nozzle segments, each including outer and inner bands withone or more nozzle vanes extending therebetween, are secured to annularouter and inner retention rings, respectively. In prior gas turbines,anti-rotation pins typically extend radially between the outer retentionring and an outwardly projecting flange on the outer band of eachsegment. These radially oriented prior anti-rotation pins encounterspace limitations which prevent removal of certain of the pins whenperforming turbine maintenance in situ. For example, at the horizontaljoint, the case is very close to the retention ring and theanti-rotation pin cannot be removed, leaving the nozzle segmentsessentially non-removable. As a consequence, maintenance and testingoperations have been found to be laborious and costly. Therefore, thereis a need to generally improve the capability for removing andinstalling nozzle segments to facilitate maintenance and testingoperations.

BRIEF DESCRIPTION OF THE INVENTION

According to a preferred aspect of the present invention, the outer bandof each nozzle segment is provided with an axially extending hole forreceiving an anti-rotation pin which can be readily removed andreplaced, enabling removal and replacement of selected nozzle segmentsin an axial direction and without the need to remove the case. Eachaxially extending anti-rotation pin extends through radially outwardlyextending slots in radial outward flanges of the outer band of thecorresponding nozzle segment and through corresponding holes in theretainer ring. Retainer plate segments overlie the end axial faces ofthe anti-rotation pins and are secured to the retainer ring. By removingthe retention plate segments, the anti-rotation pins can be removed inan axial forward direction, enabling circumferential removal andinsertion of each of the nozzle segments.

It will be appreciated that the nozzle segments have gaps betweenrespective inner and outer bands of circumferentially adjacent segmentsand which gaps are provided with seals, for example, spline seals. Thesespline seals, as well as the shape of the nozzle segments, preventdirect axial removal of the nozzle segments upon removal of theanti-rotation pins. In accordance with a preferred aspect of the presentinvention, the nozzle segments are enabled for removal in an axialdirection. Particularly, the anti-rotation pins of the selected segmentand nozzle segments adjacent the selected segment are removed in anaxial direction and the adjacent segments are stacked in acircumferential direction away from the selected nozzle segment. In thismanner, the gap distances between adjacent segments are eliminated andan enlarged gap is opened between the selected segment and an adjacentsegment, enabling axial removal of the selected segment. Theanti-rotation pins and retention plate segments are removable withoutremoving the case. To replace the segment the foregoing procedure isreversed.

In a preferred embodiment according to the present invention, there isprovided a retention system for nozzles of a turbine, comprising anozzle retention ring for disposition about an axis of the turbine, aplurality of circumferentially adjacent nozzle segments carried by thenozzle retention ring and anti-rotation pins extending in generallyaxial directions and engaging between the retention ring and the nozzlesegments, respectively, to restrain movement of the nozzle segments in arotational direction about the turbine axis.

In a further preferred embodiment according to the present invention,there is provided a method of removing in an axial direction a selectednozzle segment of an annular array of nozzle segments forming a stage ofa turbine from a retention ring carrying the annular array of nozzlesegments, comprising the steps of (a) removing in a generally axialdirection substantially axially extending pins from a plurality ofnozzle segments of the annular array thereof, including the selectednozzle segment, and the retention ring, thereby releasing nozzlesegments adjacent the selected nozzle segment for sliding movement aboutan axis of the turbine in a circumferential direction away from theselected nozzle segment, (b) sliding the released nozzle segmentsadjacent the selected nozzle segment in a circumferential directionabout the axis away from the selected nozzle segment and (c) removingthe selected nozzle segment in a generally axial direction.

In a further preferred embodiment according to the present invention,there is provided a method of installing a selected nozzle segment intoan opening in an annular array of nozzle segments for forming a stage ofa turbine, comprising the steps of (a) inserting the selected nozzlesegment in a generally axial direction into the opening, (b) inserting apin in an axial direction through the selected nozzle segment and theretention ring to secure the selected nozzle segment to the nozzleretention ring, (c) sliding nozzle segments adjacent the insertedselected nozzle segment in a circumferential direction toward theselected nozzle segment into predetermined circumferential positionsabout the turbine axis and (d) securing the adjacent nozzle segments tothe retention ring in the predetermined circumferential positions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a nozzle segment for use in a stageof a gas turbine;

FIG. 2 is a fragmentary perspective view of the nozzle segments andretention ring;

FIG. 3 is a fragmentary perspective view with parts in cross-section ofthe nozzle retention ring and portions of the retention plate;

FIG. 4 is an axial end view of the retention plate segments;

FIG. 5 is an axial schematic view of nozzle segments arranged in anannular array forming a turbine stage;

FIG. 6 is a schematic axial view of a pair of adjacent segmentsillustrating the gaps and spline seals between adjacent segments; and

FIG. 7 is an enlarged fragmentary axial end view of the annular segmentsstacked one against the other, opening a gap between a selected segmentand an adjacent segment, enabling axial removal and insertion of theselected segment.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, there is illustrated a nozzle segment, generallydesignated 10, and including an outer band 12, an inner band 14 and oneor more nozzle vanes 16 extending between the outer and inner bands. Theouter bands 12 of the nozzle segments 10 are secured to an outerretention ring 18. The inner bands 14 are secured to an inner casing 20,by an annular array of inner diameter retention plates 22. The retentionplates 22 are bolted to the casing 20 with bolts, not shown, extendingin an axial direction, enabling removal of the inner diameter retentionplates 22 in an axial forward direction.

In accordance with a preferred aspect of the present invention, axiallyextending anti-rotation pins 24 are provided between the outer bands 12and the outer retention ring 18, preferably one pin 24 per segment 10.Particularly, the outer band 12 includes a pair of radially outwardlyextending flanges 30 and 32, respectively, axially spaced one from theother. Axially aligned slots are provided in the flanges and receive theanti-rotation pin 24. The retention ring 18 includes an aperture 34along an aft portion which receives one end of the anti-rotation pin 24.The opposite end of the anti-rotation pin passes through an opening 35in a flange 37 along a forward portion of ring 18 and engages in theslot of the forward flange 30 of the outer band 12. With theanti-rotation pin 24 in place, it will be appreciated that the nozzlesegment 10 is secured against rotation about the turbine axis.

To retain the anti-rotation pins 24 in positions preventing rotation ofthe nozzle segments 10 relative to the retention ring 18, an annulararray of a plurality of retention plate segments 36 are secured to andon the forward face of the retention ring 18. Particularly, an annulargroove or surface 38 is formed in the forward face 40 of the retentionring 18 and bolt holes 42 are provided in the retention ring 18 openingthrough the forward face of the groove 38. As illustrated in FIG. 4, theretention plate segments 36 have shaped portions corresponding to theshape of the grooves 38. Bolt holes 44 are provided in the segments 36.Consequently, the annular array of segments 36 may be bolted in thegroove 38 along the forward face of the retention ring 18 to overlie theanti-rotation pins 24 and thereby maintain the anti-rotation pins 24 inposition. The anti-rotation pins 24 prevent circumferential movement ofthe nozzle segments relative to the retention ring 18. It will beappreciated that by removing the retention plate segments 36, i.e., byremoving the bolts 46 securing the segments 36 to the retention ring 18,the ends of the anti-rotation pins 24 are exposed for removal in aforward axial direction. The retention plate segments 36 are preferablyprovided in lieu of an annular retention plate to enable removal of oneor more selected nozzles without removal of the entirety of the segments36 as described below. Seven retention plate segments 36 are preferred,although it will be appreciated that a fewer or greater number ofsegments 36 may be provided.

In order to remove a selected nozzle segment 55 (FIG. 5) from theannular array of nozzle segments 10 and remove the selected segment 55in an axial direction without removal of the surrounding turbine casing,one or more of the nozzle retention plate segments 36, including thesegment 36 overlying the selected nozzle 55, are removed. For example,and for illustrative purposes, there is illustrated in FIG. 5 an annulararray of forty-eight nozzle segments 10. In order to remove a selectedsegment 55, the retention plate segments 36, which overlie the selectedsegment 55 and fifteen nozzle segments 10 a-10 p to one side or theother of the selected nozzle segment 55 are removed, thereby exposingthe axially forward facing ends of pins 24. The inner diameter retentionsegments 22 of the adjacent nozzle segments are also removed from theinner case to release the inner band portions 14 of the nozzle segments10.

As illustrated in FIG. 6, the adjacent nozzle segments 10 havepredetermined gaps 50 between adjacent outer bands 12 and adjacent innerbands 14 which gaps 50 are sealed by spline seals 52. The spline seals,as well as the shape of the segments including the outer and innerbands, as illustrated in FIG. 2, preclude removal of the selected nozzlesegment 55 in an axial direction. However, by removing the retentionplate segments 36 of about fifteen adjacent nozzle segments 10, as wellas removing the anti-rotation pins 24 of each of the adjacent segments10 a-10 p including the selected segment 55, the nozzle segments 10 arereleased for circumferential rotation. The nozzle segments 10 a-10 padjacent to the selected segment 55 are then circumferentially displacedin a circumferential direction away from the selected segment 55 tostack one against the other, thus reducing or eliminating the gaps 50between the respective adjacent nozzle segments of the nozzle segments10 a-10 p. It will be appreciated that the spline seals 52 are disposedin slots 57 of the outer and inner bands with excess circumferentialspace between their circumferential edges and the interior ends of theslots 57. This enables the nozzle segments 10 a-10 p to stackcircumferentially one against the other once the anti-rotation pins 24have been withdrawn.

With the appropriate number of nozzle segments 10, e.g., segments 10a-10 p, stacked one against the other away from the selected segment 55,a gap 54 (FIG. 7), at least equal in circumferential extent to the gaps50 between the released and circumferentially moved nozzle segments 10a-10 p is opened between the selected segment 55 and the adjacentsegment 10 a. The gap 54 is sufficient to permit the spline seals 52 tobe removed and the selected nozzle segment 55 displaced axially forremoval. Any one or more of the circumferentially displaced nozzlesegments 10 a-10 p can likewise be removed by displacement of thesegments in a circumferential direction toward the opening left by theremoved segment 55 to open a gap sufficient to enable removal of afurther selected nozzle segment. As a specific example, the typical gapbetween adjacent segments is 0.003-0.0060 of an inch. The spline seals52 are about ¾-inch wide. Hence, the stacking of the adjacent segments10 a-10 p against one another in a direction away from the selectedsegment 55 enlarges the gap between the selected segment 55 and thenext-adjacent segment 10 a to the cumulative extent of the gaps whichare closed between adjacent segments.

Once the selected nozzle segment 55 or segments have been refurbished orrepaired, or new segments are provided, the procedure can be reversed.For example, the refurbished or new nozzle segment can be insertedaxially to bear against the retention ring 18 and the inner casing 20.The anti-rotation pin 24 is then inserted through the aligned holes 30and 32 of the retention ring 18 and the slots in the outer flanges 30and 32 of the outer band of the axially inserted segment. The adjacentsegments 10 a-10 p can then be sequentially displaced circumferentiallytoward the inserted segment to align the holes 34, 35 and slots offlanges 30, 32 at each circumferential nozzle segment location. Theanti-rotation pins 24 are then inserted into the aligned holes and slotsof the circumferentially displaced nozzle segments 10 a-10 p, therebyfixing their circumferential position. The inner diameter retentionplates 22 are also secured to the casing 20, securing the inner bands 14to the casing 20. The retention plate segments 36 are bolted to theaxial face of the retention ring 18 to overlie the forwardly facing endsof the anti-rotation pins 24. The retention plate segments 36 thusmaintain those pins in position, securing the nozzle segments 10 againstrotation.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. A retention system for nozzles of a turbine, comprising: a nozzleretention ring for disposition about an axis of the turbine; a pluralityof circumferentially adjacent nozzle segments carried by said nozzleretention ring; and anti-rotation pins extending in generally axialdirections and engaging between said retention ring and said nozzlesegments, respectively, to restrain movement of the nozzle segments in arotational direction about the turbine axis.
 2. A system according toclaim 1 wherein said retention ring includes an axially facing surface,said anti-rotation pins being exposed through said surface and at leastone retention plate segment overlying the axially facing surface,precluding removal of the pins in an axially direction.
 3. A systemaccording to claim 2 wherein said retention plate segment comprises oneof a plurality of arcuate retention plate segments arranged in anannular array thereof about the axis.
 4. A system according to claim 2wherein each of said nozzle segments includes an outer band and a pairof axially spaced apertures, said retention ring having aligned openingswhereby each said pin is received in said apertures and said openings.5. A system according to claim 2 wherein said retention plate segmentcomprises one of a plurality of arcuate retention plate segmentsarranged in an annular array thereof about the axis, said arcuateretention plates being bolted to said retention ring.
 6. A method ofremoving in an axial direction a selected nozzle segment of an annulararray of nozzle segments forming a stage of a turbine from a retentionring carrying the annular array of nozzle segments, comprising the stepsof: (a) removing in a generally axial direction substantially axiallyextending pins from a plurality of nozzle segments of the annular arraythereof, including the selected nozzle segment, and said retention ring,thereby releasing nozzle segments adjacent said selected nozzle segmentfor sliding movement about an axis of the turbine in a circumferentialdirection away from the selected nozzle segment; (b) sliding thereleased nozzle segments adjacent said selected nozzle segment in acircumferential direction about the axis away from the selected nozzlesegment; and (c) removing the selected nozzle segment in a generallyaxial direction.
 7. A method according to claim 6 wherein said nozzlesegments are spaced from one another about the axis to define gapsbetween adjacent nozzles and step (b) includes sliding said adjacentnozzle segments in the circumferential direction away from the selectednozzle segment to stack the adjacent nozzle segments one against theother and thereby open a gap between said adjacent nozzle segments andsaid selected nozzle segment enabling removal of said selected nozzlesegment in said generally axial direction.
 8. A method according toclaim 6 wherein said nozzle segments are spaced from one another aboutthe axis to define gaps between adjacent nozzles and step (b) includesstacking said adjacent nozzle segments one against the other in thecircumferential direction away from the selected nozzle segment to closethe gaps between said adjacent segments and open a gap between theselected nozzle segment and said adjacent nozzle segments of sufficientcircumferential extent to enable removal of the selected nozzle segmentin the generally axial direction.
 9. A method according to claim 6including removing at least one inner diameter retention plate from aninner casing to release an inner band of said selected nozzle segment toenable removal of the selected nozzle segment in the generally axialdirection.
 10. A method according to claim 6 including securingretention plate segments to said retention ring to overlie said pins andprevent removal of said pins in said substantially axially extendingdirection.
 11. A method according to claim 6 including, prior to step(a), removing at least one retention plate segment overlying saidanti-rotation pins to enable the pins for removal in said substantiallyaxial direction.
 12. A method of installing a selected nozzle segmentinto an opening in an annular array of nozzle segments for forming astage of a turbine, comprising the steps of: (a) inserting the selectednozzle segment in a generally axial direction into said opening; (b)inserting a pin in an axial direction through the selected nozzlesegment and the retention ring to secure the selected nozzle segment tothe nozzle retention ring; (c) sliding nozzle segments adjacent theinserted selected nozzle segment in a circumferential direction towardsaid selected nozzle segment into predetermined circumferentialpositions about the turbine axis; and (d) securing said adjacent nozzlesegments to said retention ring in said predetermined circumferentialpositions.
 13. A method according to claim 12 wherein step (d) includesinserting pins in an axial direction through said adjacent nozzlesegments and the nozzle retention ring to secure the adjacent nozzlesegments to said nozzle retention ring.
 14. A method according to claim12 including, prior to step (a), releasing the adjacent nozzle segmentsfrom the nozzle retention ring for sliding movement about the axis ofthe turbine in the circumferential direction and sliding the adjacentnozzle segments in a circumferential direction about the axis to providesaid opening in the annular array of said nozzle segments.
 15. A methodaccording to claim 12 and, subsequent to step (d), securing a pluralityof inner diameter retention plates to a casing of the turbine to retaininner diameter band portions of the nozzle segments in the turbine. 16.A method according to claim 12 including, subsequent to step (d),securing at least one retention plate segment to said retention ringoverlying an axially facing end of said pin.
 17. A method according toclaim 16 including inserting pins in a generally axial direction throughsaid adjacent nozzle segments and said retention ring to secure theadjacent nozzle segments to said retention ring, and securing at leastone retention plate segment to said retention ring in overlying relationto an axial end face of said pins to retain said pins in positionssecuring the adjacent nozzle segments and retention ring to one another.